Machines such as trolley-assist vehicles or electric locomotives generally employ a pantograph assembly to provide electric power to the machine. Typically, the pantograph assembly is carried on top of the machine. The pantograph assembly is configured to draw electrical power from an overhead conductor and transfer the power to the machine. On machines such as off highway trucks, the pantograph assembly is raised and lowered to make connection with the overhead conductors. When the pantograph is lowered and the machine travels over an uneven work surface, the components of the pantograph assembly may be jostled, thereby creating stresses in the components and the actuation mechanisms that control the raising and lowering of the pantograph assembly.
U.S. Pat. No. 1,844,586 issued to McLaughlin on Jul. 23, 1931, teaches a hold down device for a pantograph assembly. One type of hold down device contemplated by McLaughlin comprises generally a crank arm fixed on an actuating shaft, and a hook pivotally mounted at a pivot pin on the crank arm. Rotation of the actuating shaft in one direction causes the hook to be swung into engagement with the stirrup on an upper link of the pantograph, and then move downward in a substantially vertical direction. The hook is spring-pressed against the stirrup so that there is no danger of the hook becoming disengaged from the stirrup. The actuating shaft imparts both rotary and translational motion to the hook and the hold down device locks the pantograph in the collapsed position, and depresses the upper links of the pantograph to the limit of their downward movement. Despite the teaching by the McLaughlin patent, not all locking mechanisms provide complex motion that locks the pantograph in the collapsed position and limits movement of its components.